1. Field of the Invention
The present invention relates to a communication apparatus connectable to a network.
2. Description of the Related Art
There has been a well-known information processing system provided with a power saving mode that reduces power consumption by going into a standby mode. An example of this information processing system is a communication system including an information processing apparatus, which is a main body side with a main CPU, and a discrete network interface card (NIC) with a sub CPU. In such a communication system, during its power saving mode, generally, the information processing apparatus on the main body side is switched to a power saving mode while the modules on the NIC side that consume less electric power are put in standby state with electric power remaining to be supplied thereto from the normal power supply.
The communication system (more specifically, the main body side) returns to the normal power mode in response to an event that a predetermined condition has been met in the power saving mode. An example of the predetermined condition is that a packet matching the condition for returning to the normal power mode has been received from the network. To enable such a packet to be received, even if power supply is switched to the power saving mode, power is kept being supplied to the NIC, and the connection (link) to the hub (a local area network (LAN) switch) is maintained.
Meanwhile, some recent NICs support a communication speed of 1000 Mbps (megabits per second) (1 Gbps (gigabits per second)) in addition to the conventional speeds of 10 Mbps and 100 Mbps. However, in a communication mode at 1000 Mbps, power consumption of an NIC is higher than that at 10 Mbps or 100 Mbps. As is widely known, there is a method capable of reducing power consumption in power saving mode by re-establishing the link to the network at 10 Mbps or 100 Mbps when power supply is switched from the normal power mode to the power saving mode.
For example, Japanese Patent Application Laid-Open No. 2004-243533 discusses how a media access control (MAC) of an image forming apparatus determines a communication speed to suit a communication performance of a hub when the power supply is switched to an energy saving mode while the image forming apparatus is connected to the hub.
Japanese Patent Application Laid-Open No. 2002-271334 reveals how to change a communication speed of one's own apparatus to a slower set communication speed if no information has been exchanged for a predetermined length of time between a host computer and an NIC connected to a LAN.
As an authentication standard to authenticate connections to the LAN, for example, IEEE 802.1X is well known. Connections to the LAN are limited by authentication to prevent those other than predetermined terminal devices from connecting to a computer network.
In an environment where callers are to be authenticated by an authentication system, such as IEEE 802.1X, when power supply is switched to a power saving mode by the above-described method, if the communication speed is changed, a situation occurs as follows.
More specifically, after the link was disconnected (link down) to change a communication speed, if the communication speed setting has been changed and a link has been established again (link up), it is determined that a new NIC has been connected to the network, so that this connection is to be authenticated anew.
Therefore, although the communication speed has been changed by performing link up and link down, if power supply has been switched to the power saving mode without performing an authentication process, even after the switch to the power saving mode, authentication is to be performed anew. In other words, in order to execute an authentication process, power supply is to be returned from the power saving mode to the normal power mode, which means that full power saving effects cannot be obtained.
After the communication speed has been changed by generating a link down and a link up status, even if an authentication process is started before power supply is switched to the power saving mode, there is a possibility that a similar situation as described above arises. In the above-described authentication process, since information is to be exchanged between the LAN switch and the authentication server on the network, a certain length of time is consumed depending on network traffic density and load status of the LAN switch and the authentication server. When power supply has been switched to the power saving mode while an authentication process is in progress, immediately after this switch of power supply mode, a packet related to the authentication process is to be received from the LAN switch or the authentication server. This initiates immediate return to the normal power mode. To put it simply, sufficient power saving effects cannot be obtained.